I'm trying to work on a computer for a client who lost their administrator password. Right now, we only have access to the 'guest' account and the 'userxxx' account on Windows Vista Home Premium. Here's the stuff I tried:

The default and only user is unable to access due to lost password. I am aware of Vista's 'hidden' administrator account, but I am unable to activate it using the command prompt since it gives me access denied. I can't run the command prompt as an administrator because UAC wants the password for the user-admin. Booting up into safemode also doesn't get the default administrator account to appear, only the user-admin and guest accounts.

Can't disable UAC without it prompting me for the password, can't access the registry key to disable it without the password either. I can't do anything from the guest account without (understandably) using the admin password.

I also tried ophcrack and was unable to crack the password from that. It came up as 'not found'.

Short of reinstalling windows, Not sure what else can be done. I'm 100% sure that the hidden admin account in Vista does not have a password, but I can't seem to enable the option to log onto the darned thing. I know it's there, as the command prompt lists the three accounts with 'net user', but is denying my rights to enable the Administrator. Anyone have any suggestions for this? I would rather not swipe the hard drive unless absolutely necessary.

You can download the file from the same site and burn it to a CD or a USB stick; then boot to that. Follow the instructions carefully to remove the Administrator password (basically making it blank) and then reboot, log in as Administrator, and set the password to something that makes sense.